1. Field of the Invention
The present invention relates to an image processing apparatus utilizing a digital differential analyzer (referred hereafter as DDA) method of processing and, more particularly, to a mechanism of processing fractional data in such an image processing apparatus.
2. Description of the Background Art
Conventionally, processing of image data has been performed in series, bit by bit. But, with this manner of processing it has been difficult to improve a speed of processing.
As a solution to this situation, developement of processing of image data in parallel, byte by byte, has been in progress.
Now, in incorporating such a processing of image data in parallel into an image processing apparatus, mechanisms of contraction of image data are indispensable because output of image processing is to be transmitted to a CRT, a printer, or likes. Moreover, contraction of image data for the sake of selective extraction of a part of image data is also considered to be highly desirable.
A most common method of such contraction of image data has been a DDA method. However, use of the DDA method in the image processing apparatus of parallel processing type unavoidably gives rise to appearances of fractional image data due to the fact that the selective extractions are to be performed in any desired number of bit. For example, as shown in FIG. 1, when a contraction to one quarter is performed by using a DDA pattern D, a contracted image data C can be obtained in which only shaded bit spaces corresponding to "1" in the DDA pattern D is valid. However, when the contracted image data C does not have a number of bit spaces which is an interger multiple of the number of bit spaces in one byte, as in FIG. 1, a fractional image data F appears. In FIG. 1, the missing two bit spaces are also indicated by a dotted line.
Thus, such an image processing apparatus of parallel processing type using DDA method is necessarily to be equipped with a mechanism for processing fractional image data properly. But, making such a mechanism for processing fractional image data by conventional hardware structures requires an enormously complicated configuration.